# Section 1: The Nature of Energy

• What is energy?

• Every change that occurs—large or small—involves energy.

• When something is able to change its environment or itself, it has energy.

• Energy is the ability to cause change.

• Energy can be stored and it can move from place to place.

• Radiant energy from the Sun travels a vast distance through space to Earth, warming the planet and providing energy that enables green plants to grow.

• Kinetic Energy: the energy a moving object has because of its motion.

• The kinetic energy of a moving object depends on the object’s mass and its speed.

• Joule: The SI unit of energy

• Potential Energy: Stored energy due to position

• Energy doesn’t have to involve motion.

• Elastic Potential Energy: energy stored by something that can stretch or compress, such as a rubber band or spring.

• Chemical Potential Energy: Energy stored in chemical bonds

• Gravitational Potential Energy: energy stored by objects due to their position above Earth’s surface.

• According to the equation for gravitational potential energy, the GPE of an object can be increased by increasing its height above the ground.

• An object’s gravitational potential energy increases as its height increases.

# Section 2: Conservation of Energy

• Changing Forms of Energy

• A lightbulb is a device that transforms electrical energy into light energy and thermal energy.

• Fuel stores energy in the form of chemical potential energy.

• In the engine of a car, several energy conversions occur.

• Some energy transformations are less obvious because they do not result in visible motion, sound, heat, or light.

• Conversions Between Kinetic and Potential Energy

• To understand the energy conversions that occur, it is helpful to identify the mechanical energy of a system.

• Mechanical Energy: the total amount of potential and kinetic energy in a system and can be expressed by this equation.

• Mechanical energy is energy due to the position and the motion of an object or the objects in a system.

• Energy transformations also occur during projectile motion when an object moves in a curved path.

• Objects that can fall have gravitational potential energy.

• The Law of Conservation of Energy: states that energy cannot be created or destroyed.

• Mechanical energy stays constant.

• Kinetic and potential energy simply change forms and no energy is destroyed.

• Energy can change from one form to another, but the total amount of energy never changes.

• The law of conservation of energy requires that the total amount of energy going into a hair dryer must equal the total amount of energy coming out of the hair dryer.

• The law of conservation of energy is a universal principle that describes what happens to energy as it is transferred from one object to another or as it is transformed.

• Sometimes it is hard to see the law of conservation of energy at work.

• The total amount of energy always stays the same.

• A special kind of energy conversion—nuclear fusion—takes place in the Sun and other stars.

• Mass is converted to energy in the processes of fusion and fission.

• Another process involving the nuclei of atoms, called nuclear fission, converts a small amount of mass into enormous quantities of energy.

• In either process, fusion or fission, mass is converted to energy.

• In processes involving nuclear fission and fusion, the total amount of energy is still conserved if the energy content of the masses involved are included.

• The process of nuclear fission is used by nuclear power plants to generate electrical energy.

• The Human Body - Balancing the Energy Equation

• Some of the chemical potential energy stored in your body is used to maintain a nearly constant internal temperature.

• A portion of this energy also is converted to the excess heat that your body gives off to its surroundings.

• The complex chemical and physical processes going on in your body also obey the law of conservation of energy.

• Your body stores energy in the form of fat and other chemical compounds.

• To maintain a healthy weight, you must have a proper balance between energy contained in the food you eat and the energy your body uses.

• Your body also can use the chemical potential energy stored in fat for its energy needs.

• Every gram of fat a person consumes can supply 9 C of energy.